This invention relates to an external boneanchoring element, or fixator.
External anchoring of bones is an old surgical technique which is particularly useful for long bones such as the femur, the tibia, the humerus, the radius, the cubitus and the bones in the leg. Available types of fixators enable two kinds of bone-anchoring to be carried out: non-transfixing anchoring, wherein pins are introduced into the bone without completely transversing it, and transfixing anchoring, which is mostly used on the leg and is more rigid than non-transfixing anchorage, wherein the pins traverse the bone and extend from one side of the limb to the other. In transfixing anchoring, two rods or frames fitted at both sides of the limb are anchored on two groups of pins disposed on either side of the fracture. The two frames or rods are stabilized by a brace interconnecting them, and may comprise sliding rods or bars, the length of which can be increased or reduced. Similar devices are used in non-transfixing anchoring, except, of course, the device is fitted at only that side of the fractured limb from which the pins extend.
External fixators of this general type commercially available from several companies, including EBI Medical Systems, Inc., Zimmer and Richards Medical Company, structurally are relatively complex and correspondingly costly to manufacture, and of those known to applicant, are inconvenient to use by reason of the need for a multiplicity of tools such as wrenches, including Allen wrenches of different sizes, in order to apply the fixator to the patient and/or to achieve compression/distraction adjustment.
Specialized versions of this type of external fixator for treatment of comminuted displaced fractures of the distal radius and ulna are also available from Richards ("Colles Fracture Frame") and Zimmer ("Clyburn Dynamic Colles Fixator"). Both devices immobilize the fractured distal radius by two holding pins in the metacarpal bones and two parallel pins in the radius, and each has a universal joint intermediate the two pairs of holding pins which may be adjusted to permit early motion of the wrist while still maintaining distraction and proper alignment of the fracture. However, partly because both employ a form of turnbuckle, application and adjustments of the Richards device involve the use of a hex wrench (Allen wrench with handle) and two open-end wrenches, and two knurled adjustng nuts and a hex wrench are involved in the adjustment of the Zimmer device. Both devices are complicated in their construction and manipulation and are, therefore, not only costly to manufacture but do not permit the convenient setting of the fracture nor the axial adjustment necessary to enable the bone fragments to be moved away or towards each other (retraction or compression).